Frame made of a composite material, especially for the fuselage of an aircraft, and its method of production

ABSTRACT

In order to reinforce a working hull, such as the fuselage of an aircraft and in particular that of a helicopter, a frame (C) is embodied made of a composite material in the form of a monolithic monobloc structure. This structure is constituted by a profile whose internal flange (16) and the external half-flanges (18) principally comprise unidirectional fibers which extend over its entire length. As a variant, the lower section of the frame is embodied separately in the form of a panel bordered over its entire periphery by lateral half-flanges which also principally comprise unidirectional fibers. After assembling the two sections of the frame, the half-flanges are then opposite each other in the elongation.

FIELD OF THE INVENTION

The invention concerns a frame made of a composite material intended toreinforce a structure, such as the fuselage of an aircraft and inparticular that of a helicopter. The invention also concerns a method toproduce such a frame.

BACKGROUND OF THE INVENTION

In rotary wing aircraft, such as helicopters, and fixed wing aircraft,the fuselage, whose structure is essentially a hull, may be required tobear localized stresses requiring the presence of one or more frames todistribute these stresses inside the working structure. In the case of ahelicopter, frames such as these, especially reinforcement frames, areusually used for fixing the engine or engines and the transmission unitsto the rotor on the top of the fuselage. In fixed wing or rotary wingaircraft, reinforcement frames may also be used to fix the resistantelements of the undercarriage.

As shown in detail in the document FR-A-2 539 701, the method is knownfor producing the fuselage of a helicopter and in particular thereinforcement frames of this fuselage made of a composite materialconstituted by carbon fibers embedded in a plastic mould.

In this document, each of the frames includes two vertical struts andtwo horizontal crosspieces whose extremities are fixed to theextremities of the vertical struts. The struts and the crosspiecescomprise a casing made of a composite material encompassing ahoneycomb-shaped material. More precisely, the casing of the verticalstruts has a cross section in the form of a high-shaped cap closed tothe outside by a composite strip, whereas the casing of the horizontalcrosspieces is formed of two U-shaped sections disposed back-to-back andconnected by two composite strips. The assembling between the lateralbeams and the horizontal beams is effected by glueing by making theextremities of the vertical struts penetrate into the recessed sectionsof the extremities of the horizontal crosspieces.

A reinforcement frame embodied in this way presents a number ofdrawbacks. Thus, the conception described only makes it possible toembody frames whose shape is approximately rectangular and is notapplicable to frames having a different shape, said shape being, forexample, circular or polygonal. Furthermore, the segmenting into threeelements of the upper portico-shaped section of the frame results indiscontinuities in the transmission to the entire frame structure oflocalized stresses applied to the latter, for example at locations usedfor the fixing of the main transmission box or the resistant devices ofthe undercarriage. Moreover, the positioning of the braces bearing theselocalized stresses has not been proved to be satisfactory. Finally, theflanges of the vertical struts of the frame are suddenly interruptedwhen these struts are connected onto the lower beam, which increases thestructural discontinuity of the frame.

In addition, the document U.S. Pat. No. 4,593,870 describes a structuredesigned to constitute the lower part of the fuselage of an aircraft,such as a helicopter. This structure includes two webs made of acomposite material between which placed is an alveolar material. In thelower part of the structure, the webs present deformations constitutingthe starts of folding bucklings when the structure of the fuselage iscompression-stressed in a vertical direction under the effect of animpact of this structure at high speed.

SUMMARY OF THE INVENTION

The main object of the invention is to provide a structural frame madeof a composite material, in particular for the fuselage of an aircraft,designed to overcome the drawbacks of the reinforcement frame describedin the document FR-A-2 539 701, this frame able to have any shape andmaking it possible to provide improved transmisison in the web andflanges of the frame of localized stresses exerted on the braces fixedto this frame, as well as rendering it easier to place these braces.

According to the invention, this result can be obtained by means of aframe for the working hull, especially for the fuselage of an aircraft,wherein it has at least partly a monolithic structure constituted by asection made of a composite material formed of fibers with highmechanical resistance agglomerated by a hardened synthetic resin andpresenting as a section an internal flange, two external half-flangesand two webs connecting the internal flange to each externalhalf-flange, the internal flange and the external half-flanges beingmainly constituted by laps of unidirectional fibers extendinglongitudinally without discontinuity inside the section and the webs ofthe section being formed by fabrics made up of multidirectional fibersand connecting the internal flange to each external half-flange.

This configuration makes it possible to provide good stability onbuckling of the frame in the two main planes, allows for its embodimentby moulding and facilitates the installing of braces for introducingstresses and fixing the working casing of the hull.

Advantageously, the two webs connecting the internal flange to the twoexternal half-flanges form between them an acute angle open between thetwo external half-flanges and the internal flange and the externalhalf-flanges are perpendicular to a plane of symmetry of the framecontaining the bisector of said acute angle.

The monolithic structure thus defined may constitute a monoblocstructure forming all of the reinforcement frame. On the other hand,when it is necessary to provide one lower part of the frame withcharacteristics enabling it to ensure absorption of the energy inducedby the impact of the frame against the ground, only one upperportico-shaped part of the frame presents a monolithic structure.

In this case, the lower crosspiece-shaped part includes a panel borderedover its entire periphery with two lateral half-flanges.

Preferably, each lateral half-flange principally contains unidirectionalfibers extending without discontinuity over the entire length of thepanel forming the lower crosspiece.

In this case, the panel includes two parallel webs formed of fabrics ofmultidirectional fibers and delimiting between them a space filled witha ductile material, such as foam or an alveolar material. Deformationsare preferably formed in the lower parts of the webs of the panel alonga longitudinal direction of the lower crosspiece-shaped part so as tofacilitate the absorption of energy in the event of impact.

So as to ensure the assembling of the two parts of the frame withoutinterrupting the continuity of the half-flanges constituting the outsideof the latter, the upper portico-shaped part includes extremitiesdeprived of flanges fixed in recesses formed in extremities of the panelforming the lower crosspiece and opening between the lateralhalf-flanges so that the latter are located in the elongation of theexternal half-flanges of the upper portico-shaped part.

The object of the invention is also to provide a method to produce aworking hull frame, especially the fuselage of an aircraft, wherein theframe is at least partly embodied in the form of a monolithic structureby:

the draping of unidirectional and multidirectional fabrics impregnatedwith resin over a form delimiting the outer contour of a profile havingas a section an internal flange, two external half-flanges and two websconnecting the internal flange to each external half-flange, these websforming between then an acute angle open between the externalhalf-flanges, the unidirectional fabrics forming the internal flange andthe external half-flanges and the multidirectional fabrics connectingthe internal flange to each external half-flange and forming the webs ofthe profile;

the closing of a mould comprising said form, inflatable bladders and acounter-form;

the inflating of the bladders so as to compress the fabrics andheat-polymerize the resin impregnating the fabrics;

removing said monolithic structure from the mould.

BRIEF DESCRIPTION OF THE DRAWINGS

There now follows a description, given by way of example in no wayrestrictive, of two embodiments of the invention with reference to theaccompanying drawings in which:

FIG. 1 is a perspective view with dentelations representing a monoblocmonolithic reinforcement frame produced in accordance with a firstembodiment of the invention;

FIG. 2 is a cross section of the frame of FIG. 1, the structure of theflight deck and a fixing attachment being shown by the dot-and-dashlines;

FIG. 3 is a perspective and cutaway cross sectional view representing amould being used for the production of the reinforcement frame accordingto the invention;

FIG. 4 is a perspective view illustrating the putting into place of thevarious layers of fabrics constituting the webs of the section formingthe frame in the bending inward zones of the latter inside the mould ofFIG. 3;

FIG. 5 is a perspective view similar to that of FIG. 1 and illustratinga second embodiment of the invention in which the reinforcement frameincludes an upper portico-shaped monolithic part and a lowercrosspiece-shaped part embodied separately;

FIG. 6 is a cross section and perspective view of the lowercrosspiece-shaped part of the frame of FIG. 5;

FIG. 7 is a perspective and cutaway cross section view representing amould used for the production of the lower crosspiece-shaped part shownon FIG. 6;

FIG. 8 is a front view illustrating the linkage of the extremities ofthe upper portico-shaped part onto the extremities of the lowercrosspiece-shaped part; and

FIGS. 91, 9B and 9C are sections along the lines A--A, B--B and C--C ofFIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a frame C made of a composite material intended toreinforce the hull constituting the fuselage of an aircraft, such as ahelicopter. In the embodiment shown, this frame roughly has the shape ofa rectangle whose angles are rounded. However, it shall be understoodthat the technique for embodying this frame according to the inventionenables it to be given any other form adapted to the envisagedapplication, such as a circular or polygonal shape.

In the embodiment represented on FIG. 1, the frame C is fully embodiedin a monolithic monobloc form. According to the invention, thismonolithic structure is constituted by a section made of a compositematerial. The profile constituting the frame C includes an upperhorizontal portion C1 whose extremities are extended by twoapproximately right angle curved portions C2 orientated towards thebottom and themselves extended by two approximately vertical portions C3having slight concavity towards the inside of the frame and being ofequal length. The lower extremities of the portions C3 are extended bytwo approximately right angle curved portions C4 themselves extended bya lower horizontal portion C5 closing the frame. The frame thusconstituted has a vertical plane of symemetry approximately merged withthe plane of FIG. 1.

The structure of the profile constituting the frame C shall now bedescribed in more detail by referring to FIG. 2, which diagrammaticallyshows on a larger scale a cross section of this profile in the upperhorizontal portion C1.

As shown by the section of FIG. 2, the profile constituting the frame Chas an internal flange 16, two external half-flanges 18 and two webs 20connecting the internal flange 16 to each of the external half-flanges18.

More precisely, the internal flange 16 comprises a central part locatedbetween the webs 20 and wings which laterally project beyond the webs20. Also, the flange 16 is delimited interiorally by a surface 16aperpendicular to the vertical plane of symmetry of the frame definedpreviously. The surface 16a is thus flat in the portions C1 and C5 ofthe frame.

The webs 20 are orientated outwardly from the internal flange 16 and areprogressively moved away from the vertical plane of symmetry of theframe along two directions symmetrical with respect to this plane anddelimiting between them a very small acute angle open towards theoutside of the frame between the two external half-flanges 18. Thus, thebisectrix of the angle formed by the webs 20 is contained within theplane of symmetry of the frame.

The external half-flanges 18 are disposed inside the elongation of eachof the webs 20 and are orientated along a direction perpendicular to thevertical plane of symmetry of the frame by moving them away from thisplane. The half-flanges 18 are delimited towards the outside of theframe by surfaces 18a perpendicular to the vertical plane of symmetry ofthe frame and located opposite each other in the elongation. Thus, inthe rectilinear portions C1 and C5 of the frame, the outer surfaces 18aare flat surfaces.

The section of the profile constituting the frame C is uniform over theentire periphery of the latter. However, the lengths of the webs 20 maydiffer between the various portions C1 to C5. Thus as shown on FIG. 1,the length of the webs 20 may assume its largest value in the lowerportion C5, its smallest value in the portions C3, and an intermediatevalue in its upper part C1. In this case, the change of length of thewebs is effected progressively in the curved portions C2 and C4. On theother hand, the dimensions of the internal flange 16 and the externalhalf-flanges 18 are the same over the entire periphery of the frame.

The particular section of the profile constituting the monolithicmonobloc frame of FIG. 1 makes it possible to ensure good stability tobuckling of the structure thus constituted.

Furthermore and as shown by the dot-and-dash lines on FIG. 2, thissection allows for easy putting in place and positioning of the braces22 to be used in particular for the fixing of the main transmission boxwhen the frame equips a helicopter. In fact, the braces 22, which aregenerally metallic, then comprise a section 22a complementary to therecess formed between the webs 20 and whose placing inside this recessimmediately ensures correct positioning of the brace inside the verticalplane of symmetry of the frame.

The fixing braces 22 also comprise in a known way two wings 22b to beapplied to the outer faces 18a of the external half-flanges 18. Fixingof the braces is ensured by any suitable means, such as bolts or rivetstraversing both the wings 22b of the braces and the externalhalf-flanges 18 of the profile constituting the frame.

As also represented by the dot-and-dash lines on FIG. 2, the externalhalf-flanges 18 of the profile constituting the frame C are also used tofix the working casing of the hull structure 24 of the aircraft, itselfalso generally being made of a composite material. To this effect, thestructure 24 presents at the location of the frame C parts with lessthickness to be applied to the outer surfaces 18a of the externalhalf-flanges 18, the fixing of the structure 24 onto the latter beingprovided by any suitable means and in particular by glueing or riveting.

As already mentioned, in the embodiment of FIG. 1, the frame C isembodied in the form of a monolithic monobloc structure made of acomposite material. More precisely, the internal flange 16 and the twohalf-flanges 18 are mainly formed of unidirectional fibers 26, forexample in the form of bands or strips of fabrics embedded in a resinmould and extending longitudinally without discontinuity inside theprofile constituting the frame. The internal flange 16 thus includes afirst core of unidirectional fibers 26 extending over the entire widthof the flange close to the surface 16a, and a second core of fibers 26extending between the webs 20 to the base of the latter. Similarly, eachexternal half-flange 18 includes a core of unidirectional fibers 26extending over the entire width of the half-flange.

The rest of the profile constituting the frame C, that is mainly thewebs 20 and the parts of the flange 16 and of the half-flanges 18encompassing the cores of unidirectional fibers 26, is made up offabrics of bidirectional fibers 28 embedded in a resin mould.

The nature of the unidirectional fibers 26 and the fibers constitutingthe fabrics 28, as well as the nature of the resin in which these fibersare embedded, are selected according to the envisaged application fromthose fibers and resins normally used in composite materialapplications. Accordingly, the fibers may be carbon fibers and the resinmay be a duroplastic resin, such as a phenolic or epoxy type resin.

The monolithic monobloc frame C, which has just been described withreference with FIGS. 1 and 2, is produced in a mould shown by FIG. 3,this mould being conceived so as to allow for the compression of thefabrics impregnated with resin at the time of the cycle forheat-polymerizing the resin.

The mould represented on FIG. 3 firstly includes a form 30 whose surface30a orientated towards the inside of the mould has a shape complementaryto the outer shape of the frame C to be made. With the mould being open,the bidirectional tissues 28 and the unidirectional fibers 26preimpregnated with resin are draped over the surface 30a of the form30. This draping operation, normally effected for the production ofcomposite materials, is generally carried out by hand.

In the present case, so as to facilitate their placing, theunidirectional fibers 26 impregnated with resin are placed on a supportfilm which makes it possible to handle them as a fabric, no mechanicalfunction being involved when the production is ended. The unidirectionalfibers 26 thus may be draped as fabrics in successive layers so as toform the cores of the internal flange 16 and the external half-flanges18. This draping is carried out on the form 30 in the direction of thelength of the profile constituting the frame C without cutting ordiscontinuity. This characteristic is made possible by the fact that theflange and half-flanges are orientated perpendicular to the verticalplane of symmetry of the frame and presenting a uniform section.

The draping of the bidirectional fabrics 28 impregnated with resin isalso carried out in the direction of the width of the profileconstituting the frame C. The number of fabric layers constituting thewebs 20 and the number of layers of unidirectional fibers 26 aredetermined so as to give the profile the desired mechanical resistancecharacteristics.

The bidirectional fabrics constituting the webs 20 of the profile may bedraped from several fabric outputs according to industrialavailabilities. In this case, the continuity of the structure is ensuredby an overlapping of the fabrics. So as to avoid a significant localvariation of thickness, the coverings are offset with respect to oneanother.

Given the fact that the bidirectional fabrics which form the webs 20provide the linkage between the internal flange 16 and the externalhalf-flanges 18, the lateral edges of these fabrics are necessarilyfolded up onto the parts of the form 30 corresponding to the internalflange and the external half-flanges.

As illustrated on FIG. 4, in the curved portions C2 and C4 of the frameC, the length of the edge 28a of each fabric 28 folded up towards theinternal flange 16 is less than the length of fabric actually required.Accordingly, divergent notches 29a are made in the edge 28a of thefabric folded up onto the parts of the form 30 corresponding to thesecurved portions C2 and C4.

On the other hand, in the curved portions C2 and C4, the length of theedge 28b of each fabric 8 folded up towards the external half-flange 18is greater than the length of fabric actually required. Notches 29b arethus made in the edge 28b of the fabric folded up onto the parts of theform 30 corresponding to these curved portions C2 and C4 and the fabricexcess amounts are removed.

As also illustrated on FIG. 4, the notches 29a and especially 29b aremade so as to be offset between each layer of fabric 28 so that there isno overlapping of the notches at the time of stacking.

By referring to FIG. 3, it can be seen that, before starting to drapethe fabrics with bidirectional fibers 28 and the unidirectional fibers26 onto the form 30, placed on the latter in its central part locatedbetween the webs and corresponding to the internal flange is aninflatable bladder 32 which has initially been deflated.

When draping is ended, two armature bladders 34 are placed on both sidesof the webs 20, each of the bladders 34 also resting on thecorresponding external half-flange 18 and on the projecting wing of theinternal flange 16. These bladders are also deflated when they are putin position, but their armature enables them to keep in place thevarious layers of fabric before they are inflated.

The mould is then closed by the placing of a counter-form constituted bytwo lateral plates 36 which are secured to the outer edges of the form30 and rests on the outer faces of the armature bladders 34 and by theplacing of an internal peripheral part 38 composed of several sectionssecured to the parts 36 and which rests on the surface 16a of theinternal flange 16.

The bladders 32 and 34 are then pressurized so as to compress thevarious layers of fabrics preimpregnated with resin contained in themould and heat-polymerizing of the resin is effected by conventionaltechniques.

At the end of polymerization, the bladders are deflated and the mould isopened so as to extract the monolithic monobloc frame C shown in FIG. 1.

In a second embodiment of the invention to be described now withreference to FIG. 5, instead of being fully embodied in the form of amonolithic monobloc structure, the reinforcement frame according to theinvention is formed of two separate parts embodied separately which arethen assembled by suitable means.

More precisely, the reinforcement frame is, in this instance,constituted by an upper portico or arch-shaped section 10 and by a lowercrosspiece-shaped section 12, the adjacent extremities of these twosections being connected together by assembling means 14 so as to form aclosed frame.

In this embodiment of FIG. 5, the upper portico-shaped section 10 is aprofile made of a composite material and having according to theinvention a monolithic structure from one extremity to the other. Theprofile constituting the upper section 10 includes an upper horizontalportion 10a whose extremities are extended by two right angle curvedportions 10b orientated towards the bottom, said portions themselvesbeing extended by two vertical portions 10c parallel to each other andbeing of equal length.

The section of the profile constituting the upper portico-shaped part 10is identical to the section of the frame C previously described withreference to FIG. 2 in the case of the first embodiment of theinvention, except for the lower extremities of the vertical portions10c.

Similarly, the embodiment of the upper portico-shaped section of theframe of FIG. 5 is identical to the embodiment of the frame C describedpreviously with reference to FIGS. 3 and 4 with regard to the firstembodiment of the invention.

The structure of the lower crosspiece-shaped part 12 shall now bedescribed in more detail with reference to FIG. 6, which illustrates avertical section of this part 12.

The lower crosspiece-shaped part 12 is mainly constituted by a roughlyflat vertical panel 40 which extends between the lower extremities ofthe vertical portions 10c of the upper part 10 and whose thickness isclose to the distance separating the webs 20 of the profile constitutingthis part 10. As shown on FIG. 5, the panel 40 has the shape of arectangle whose two lower angles are truncated.

More precisely, the panel 40 has a sandwich structure, that is it ismade up two thin parallel vertical webs 44 defining between them a spacefilled with a ductile material, so that they adhere to ahoneycombed-shaped structure or foam 46.

The panel 40 is bordered over its entire periphery with two lateralhalf-flanges 42 orientated perpendicular to the panel 40 and extendingthe webs 44 by distancing them from the vertical plane of symmetry ofthe frame. The half-flanges 42 are delimited externally by surfaces 42aorientated perpendicular to this plane of symmetry and disposed oppositeeach other inside the elongation.

At the lower part of the panel 40, as in the upper part of this panel,the half-flanges 42 are orientated parallel to each other along aroughly horizontal direction so as to constitute two rigid parallelelements ensuring a compression-loading of the panel 40 evenlydistributed on the surface. Thus, in the event of accident, the greatestpossible absorption of energy is obtained.

Moreover, at each extremity of the panel 40 and in the top part of thelatter, the half-flanges 42 are orientated parallel to each other andalong a roughly vertical direction. These parts of the half-flanges 42may thus be placed inside the extension or prolongation of the externalhalf-flanges 18 of the part 10 of the frame, as shall be seensubsequently.

Preferably, the lateral half-flanges 42 have a monolithic structure witha rigid section and are mainly made up of unidirectional fibers 48embedded in a duroplastic resin mould. The fibers 48 extend withoutdiscontinuity over the entire circumference of the panel 40 so as toform a core in each half-flange 42. The webs 44 are connected to thecorresponding half-flanges 42 and are embodied by fabrics ofbidirectional fibers embedded in a resin mould. The remarks previouslymade with reference to the fibers and the resin constituting the frame Cin the embodiment of FIG. 1 and the upper part 10 of the frame in theembodiment of FIG. 5 are also applicable to the lower part 12 of theframe as regards this latter embodiment.

The lateral half-flanges 42 located at the extremities and at the bottomof the panel 40 allow for the fixing by glueing and riveting of thestructure 24 forming the working hull of the aircraft, the same applyingfor the half-flanges 18 in the upper part 10 of the frame.

Preferably, the webs 44 of the panel 40 have, in its lower part,undulations 44a orientated along a horizontal approximately longitudinaldirection between the extremities of the lower crosspiece-shaped part12. This particular structure makes it possible to obtain via the startof buckling a controlled deformation of the part 12 of the frame if thispart suddenly strikes the ground. In fact, the energy of the impact istransmitted through the bottom of the part 12 of the frame to theductile web 40 without the resistance of the web being reduced duringthe flight or in normal landing conditions.

The lower crosspiece-shaped part 12 is also embodied in a mould, asillustrated diagrammatically on FIG. 7. The general principle forproducing this part 12 is the same as that of the frame C (and of thepart 10) described previously with reference to FIG. 3 and thus shallnot be described further in detail. For purposes of clarity, there nowfollows a simple indication of the main stages of production and thevarious elements constituting the mould.

With the mould being initially open, only one form 50, whose upper face50a is complementary to one of the sides of the panel 40 bordered by oneof the half-flanges 32, is in place. The peripheral edge of this form 50is encompassed by an inflatable bladder 52 which has initially beendeflated. Then, according to the technique previously described indetail, the web 44 corresponding to this side of the panel 40 and thelateral half-flange 42 are embodied by draping. In order to facilitatethe placing of the unidirectional fibers 48 constituting the core of thelateral half-flange, the fibers 48 are preferably linked together by asupport film enabling them to be draped like a fabric. Given the factthat the flange 42 is perpendicular to the plane of symmetry of theframe, this draping can be effected without cutting or discontinuity,which guarantees the monolithic nature of the half-flanges 42.

The alveolar structure or foam 46 constituting the central part of thepanel 40 is then put in place, as well as a second form 54, possiblyconsisting of several parts and whose internal surface 54a iscomplementary to the external peripheral surface of thecrosspiece-shaped part 12. A new draping operation is carried out so asto produce the second web 44 of the panel and the second half-flange 42.

Finally, a counter-form 56, symmetrical to the form 50 and whoseperipheral edge is encompassed with an initially deflated inflatablebladder 58 and identical to the inflatable bladder 52, is placed so asto close the mould. The bladders 52 and 58 are then inflated and hotpolymerization is carried out according to conventional techniques.

The undulations 44a formed in the webs 44 are directly obtained bymoulding by virtue of complementary deformations formed in the form 50and in the counter-form 56.

After opening of the moulds of FIGS. 3 and 7, the parts 10 and 12 areassembled by means of the assembling means 14, this assembling now to bedescribed with reference to FIGS. 8 and 9.

As shown in particular on FIG. 8 and FIG. 9c, at each of the lowerextremities of the vertical portions 10c of the part 10 of the frame,the external half-flanges 18 and the parts projecting from the internalflange 16 are totally suppressed over a certain length. Also, at each ofthe longitudinal extremities of the lower part 12 of the frame, a recess60 open towards the outside is provided between the webs 44 of thepanel. The dimensions of the recesses 60 are such that the extremitiesdeprived of the flanges of the vertical portions 10c fully penetrateinto these recesses. In particular, the depth of each recess 60 isslightly greater than the thickness of the extremities of the portions10c and the webs 44 are progressively moved apart by the same angle asthat of the webs 20 so that the latter comes to be virtually housedwithout clearance in the recesses 60.

As illustrated by the sections represented on FIGS. 9A to 9C, the widthof the projecting parts of the internal flange 16 of the part 10 of theframe gradually reduces when the lower extremities of this part 10 drawnearer so as to totally disappear just before these extremitiespenetrate into the recesses 60. In addition and as can be seen on FIG.8, the thickness of these projecting parts of the internal flange 16 isreduced in the areas adjacent to the lower part 12.

In addition, the external half-flanges 18 of the part 10 are suddenlyinterrupted just before the extremities of the portions 10c penetrateinto the recesses 60 and these half-flanges 18 are placed in theelongation of the vertical parts of the half-flanges 42 of the lowerpart 12, as clearly shown on FIG. 8. Moreover, close to the extremitiesdeprived of the flanges of the portions 10c, the external half-flanges18 comprise standing back parts which progressively draw nearer to theinternal flange 16 so as to allow for the placing of a fishplate 62whose outer surface is located inside the elongation of the outersurfaces 18a of the half-flanges 18 and 42a of the half-flanges 42without discontinuity, as illustrated on FIG. 8. The fishplate, itselfmade of a composite material, is secured, for example, by bolts (notshown), firstly to the standing back parts of the half-flanges 18, andsecondly to the parts of the half-flanges 42 located at the extremitiesof the lower part 12. This thus ensures continuity of the frame externalhalf-flanges secured to the structure 24 of the working hull.

The fixing of the extremities of the part 10 into the extremities of thepart 12 may be achieved by means of bolts 64 traversing the webs 20 and44 of these two parts.

So as in particular to support the floor of the aircraft, horizontalbeams (not shown) may be fixed to the lower crosspiece-shaped part 12 ofthe frame, for example by means of angles, preferably also made of acomposite material. The fixing of these angles onto the panel 40 may beeffected by any suitable means, such as screws, rivets or by glueing. Inthe lower part of the panel comprising the undulations 44a, this fixingis effected solely by means of rivets so as to avoid a corner effectprejudicial to a controlled crushing of this panel at the time of anaccident.

Of course, the invention is not merely limited to the embodiment justdescribed by way of example, but covers all variants of this.

In particular, the bidirectional fabrics forming the webs 20 and 44 maybe replaced by multidirectional fabrics made up of threads orientatedalong three or four different directions.

What is claimed is:
 1. Frame made of a composite material for a workinghull, especially for the fuselage of an aircraft, wherein said framehas, at least in a part of its length, a monolithic structureconstituted by a profile made of a composite stratified material formedof fibers with high mechanical resistance, said fibers beingpre-impregnated by a hardened synthetic resin, said profile having insection an internal flange, two external half-flanges parallel to theinternal flange and two webs connecting the internal flange to eachexternal half-flange, the internal flange and the external half flangesmainly being constituted by laps of unidirectional fibers extendinglongitudinally without discontinuity on the whole length of the frameinside the profile, and the webs of the profile being formed by laps offabrics made up of multidirectional fibers, these laps of fabricscovering the internal flange and the external half-flanges to connectthe latter.
 2. Frame according to claim 1, wherein the two webs whichconnect the internal flange to the two external half-flanges formbetween them an acute angle open between the two external half-flangesand wherein the internal flange and the external half-flanges areperpendicular to a plane of symmetry of the frame containing thebisectrix of said acute angle.
 3. Frame according to claim 1, whereinthe profile made of a composite stratified material extends on the wholelength of the frame.
 4. Frame according to claim 1, wherein said frameincludes an upper portico-shaped part presenting a profile made of amonolithic stratified material and a lower crosspiece-shaped part whoseextremities are connected by assembling means to the internal flange,external half-flanges and webs.
 5. Frame according to claim 4, whereinthe lower crosspiece-shaped part includes a panel bordered over itsentire periphery with two lateral half-flanges.
 6. Frame according toclaim 5, wherein the lateral half-flanges are perpendicular to a planeof symmetry of the frame.
 7. Frame according to claim 4, wherein theextremities of the upper portico-shaped part are deprived of the flangeand are fixed in the recesses formed in the extremities of the panel andopen between the lateral half-flanges so that the latter are located inthe elongation of the external half-flanges of the upper portico-shapedpart.
 8. Frame according to claim 7, wherein the internal flange of theupper portico-shaped part includes projecting wings whose widthprogressively reduces close to the extremities deprived of the flangesof this upper part.
 9. Frame according to claim 7, wherein the externalhalf-flanges comprise standing back parts progressively drawing nearerto the internal flange close to the extremities deprived of the flangesof the upper portico-shaped part, fishplates being secured to thesestanding back parts of the external half-flanges and to adjacent partsof the lateral half-flanges.
 10. Frame according to claim 5, wherein thepanel includes two parallel webs delimiting between them a space filledwith a ductile material.
 11. Frame according to claim 10, whereinundulations are formed in the lower parts of the webs of the panel alonga longitudinal direction of the lower crosspiece-shaped part.
 12. Frameaccording to claim 10, wherein the lateral half-flanges are locatedinside the extension of the webs of the panel and mainly containunidirectional fibers extending without discontinuity over the entireperiphery of the panel.
 13. Frame according to claim 12, wherein fabricsof multidirectional fibers prolong each lateral half-flange and form thewebs of the panel.
 14. Frame for a working hull, especially for thefuselage of an aircraft, wherein it has in part at least a monolithicstructure constituted by a profile a made of a composite material formedof fibers with high mechanical resistance, said fibers beingagglomerated by hardened synthetic resin and having as a section aninternal flange, two external half-flanges and two webs connecting theinternal flange to each external half-flange in such a way that theinternal flange extends outward from the webs and that a recess opentowards the outside of the frame is formed between the webs, theinternal flange and the external half-flanges mainly being constitutedby laps of unidirectional fibers extending longitudinally withoutdiscontinuity inside the profile, and the webs of the profile beingformed by fabrics made up of multidirectional fibers and connecting theinternal flange to each external half-flange.